1. Field of the Invention
The present invention generally relates to the field of transportation vehicles, and more specifically, to devices to reduce aerodynamic drag of vehicles having open cavities.
2. Description of the Related Art
Open beds, cargo bays, and cavities are highly inefficient from an aerodynamic perspective. For example, in rail transport systems covering an empty open container car has been shown to reduce drag by as much as 40%. However, covering the bed or cargo bay is seldom practical due the size, the required hardware, and the effort involved. As a result, these vehicles typically operate uncovered on long journeys (up to 1000 miles for coal cars).
To provide a more detailed example of how inefficient open cargo and bays on transport vehicles, consider an example of transportation in the coal industry. Coal accounts for almost 50% of the total electricity production in the United States alone. Of the total coal consumption, almost two-thirds is carried by rail. By far the most important rail commodity, as of 2002 coal accounted for almost 44% of tonnage, 25% of carloads, and 21% of revenue. In 2002, almost 7.9 million carloads of coal were hauled via rail. Moreover, over 85% of all railroad coal shipments are carried by unit trains of 50 or more carloads. Typically, these shipments transport the coal without interruption from the loading facilities to the power plants.
Due to the increasing use of low sulfur western coal in power plants throughout the country, the average coal haul has risen significantly in recent years from 558 miles in 1992 to 696 miles in 2001. Over the same period, however, the revenue per ton-mile decreased by 23% due to the competitive environment for coal transportation created by alternate energy sources, transportation modes, and railroads.
The potential for energy savings by reducing the aerodynamic drag of coal cars is significant. A previous study of aerodynamic drag of coal cars suggests that a 25% reduction in drag of the empty cars would correspond to a 5% fuel savings for a round trip. Since coal transport consumes approximately 1.5 billion gallons of diesel fuel annually, a 5% fuel savings would total 75 million gallons per year. This corresponds to 2% of all Class I railroad fuel consumption.
Moreover, fuel consumption issues affecting open coal railcars also affects other open container transport vehicles, for example, railroad grain cars, container ships, truck trailers, and even pickups. Reducing aerodynamic drag in each of these transport vehicles would save wear and tear, save energy, and reduce overall fuel consumption.
Devices to reduce aerodynamic drag do exist, but are either too cumbersome, too costly, or a combination of both. Most prior art deals with cavity coverings. For example, open rail cars can be fitted with a soft or hard covering. However, such coverings must be manually installed resulting in increased manpower and time, which reduces productivity.
Automated soft covers eliminate or reduce the need for manpower and provide some time savings. However, automated soft covers require machinery to roll the covers over or retract the covers from the cargo bay. This machinery adds extra weight to the vehicle so that fuel savings are significantly reduced or eliminated. Further, soft coverings also are prone to quicker wear and tear so that the frequency of repair and replacement also reduce or eliminate hoped for savings. Moreover, because most open cargo and open bay vehicles are designed for long life with a minimum of moving parts, flexible covers and moving doors end up being very poor options.
In addition, hard covers also have several drawbacks. Hard covers add weight to the vehicle. The added weight requires an increased need for power to move the transport vehicle so that any fuel savings from reduction of aerodynamic drag are significantly reduced or eliminated due to the increased weight. In most instances, the added weight of a cargo-bay cover will also reduce the amount of cargo that may be transported due to weight restrictions.
From the above, there is a need for a system and process to reduce aerodynamic drag in open cargo bays and beds of vehicles, which can help energy efficiency and help realize energy savings.